Autism spectrum disorder (ASD) is highly heritable, with a 2-3% recurrence rate in siblings and a 60-90% concordance rate in monozygotic twins. However, known genetic causes—for example, single gene disorders such as Fragile-X or tuberous sclerosis, or chromosomal abnormalities—account for approximately 10% of ASD cases. Thus, the majority of cases of ASD are of unknown cause at present. Current estimates are that ASD susceptibility is conferred by numerous genes interacting with one another, as well as with environmental factors.